Sound speed is an effective parameter in designing an optimal beamformer. In conventional ultrasound imaging systems, the beamformer is designed assuming a fixed value of speed, whereas the speed in a tissue is not known precisely and also may fluctuate by a great value. The errors in estimating sound speed may lead to a severe degradation in the reconstructed image, as mainlobe width and sidelobe level of the beampattern are sensitive to the speed variations. In this paper, we consider the design of a transmit beamformer, which is robust to the speed variations. The problem is formulated as a convex optimization problem versus the covariance matrix of the excitation waveforms to obtain a beampattern with predefined mainlobe width and a minimum sidelobe level for all possible variations of speed. Then, by eigen-analysis of the obtained covariance matrix, a set of nonidentical single-carrier short-pulses for the excitation waveforms were designed. Various simulations indicate that the proposed method can yield a robust beampattern whose mainlobe width and sidelobe level almost remain constant by 10% speed variations. In contrast, the beampatterns obtained by nonrobust methods suffer extensive changes.

中文翻译：

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用于医学成像的超声阵列的稳健波形设计

声速是设计最佳波束形成器的有效参数。在传统的超声成像系统中，波束形成器被设计为假定一个固定的速度值，而组织中的速度并不精确，并且也可能有很大的波动。由于波束图的主瓣宽度和旁瓣电平对速度变化很敏感，因此估计声速时的误差可能会导致重建图像的严重退化。在本文中，我们考虑了对速度变化具有鲁棒性的发射波束成形器的设计。该问题被表述为与激励波形的协方差矩阵相对的凸优化问题，以获得具有预定义主瓣宽度和所有可能速度变化的最小旁瓣电平的波束图。然后，通过对得到的协方差矩阵进行特征分析，设计了一组不同的单载波短脉冲激励波形。各种模拟表明，所提出的方法可以产生稳健的波束图，其主瓣宽度和旁瓣电平几乎保持不变，速度变化为 10%。相比之下，通过非鲁棒方法获得的波束图会发生很大的变化。